1. Field of the Invention
This invention relates to a scanning illuminator suitable for use in high speed copying machines, said scanning illuminator being adapted to provide a distribution of illumination for compensating a distribution of loss in light quantity due to the so-called Cos.sup.4 law of lenses on the surface of an original, and including fixed sources of light.
2. Description of the Prior Art
In the prior art, it is known that when an original uniformly illuminated is projected onto a photoreceptor through a lens system, the original is subjected to underexposure at its opposite ends in comparison with its central portion under the influence of a loss in light quantity due to the Cos.sup.4 law in the lens system. In order to overcome this problem, the prior art slit-exposure scan type copying machines comprise, for example, a rod-like light source having a filament longer at its opposite ends than its central portion in a direction perpendicular to the scanning direction so that the luminance distribution will be maintained. On the other hand, there is not compensated any loss in light quantity particularly due to the Cos.sup.4 law in the scanning direction. It is desirable that the photoreceptor can be subjected to uniform exposure both in the scanning direction and the direction perpendicular thereto. Most scanning illumination systems in the prior art slit-exposure type copying machines include a scanning mirror followed by a source of light. However, the moving light source has a problem in durability since it is accompanied by electric cords or the like, and is especially unsuitable for high speed copying machines.